BOTH! ;-)
I've had head gaskets just start to fail... with
a low compression reading between 3 & 4 at cold,
but once the engine was warmed up the expansion of
thealuminum head was enough to seal it (gasket took
another month to finally open).
On Aluminum head engines, it is never a good idea to
remove sprak plugs when HOT. Ideally cold removal
only, to reduce the chance of stripped sprak plug
threads. I've I wish to do a HOT compression check,
then I will break the plugs loose at cold. Wipe
the threads with a little antisieze compound, and
reinstall. [Admitted at times I've gone out to look
at a car, only to discover the owner has already "warmed
it up" for me. - which is a good way of helping mask
some of those start up noise. ;-)]
Cheers,
Tom Walter
Austin, TX. (suffering from a head cold,and too many typos)
P.S. How many of you have a leak down tester?
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